Synthesis and Oxygenation of a Nickel(II) and Zinc(II) Dithiolate:  An Experimental and Theoretical Comparison

Abstract

The diamino-dithiolato N2S2 ligand N,N'-bis-2-methyl-mercaptopropyl-N,N'-dimethylethylenediamine, H2bmmp-dmed), and its nickel (1) and zinc (2) complexes have been prepared and their reactivities with hydrogen peroxide investigated. Complex 1 yields a mixture of sulfenato (RSO-), 4, sulfinato (RSO2-), 3, and sulfonato (RSO3-), 5, products upon addition of H2O2. Products are separable by column chromatography. Stoichiometric addition of H2O2 to 2 yields an inseparable mixture. Excess peroxide addition results in oxygenation of the ligand to the disulfonate, 6, and decomplexation of zinc. Complexes 1, 2, and 3 and compound 6 have been investigated by X-ray crystallography, and their structures are reported. Density functional theory (DFT) calculations of 1 and 2 reveal significant sulfur p character in the HOMO of each complex. However, 1 also shows significant metal d character that is pi-antibonding with respect to the sulfur p orbitals. Complex 2 shows little metal character in the HOMO. Implications of the HOMO with respect to S-centered reactivity and metal ligand distances in S-oxygenated products are provided.

Nickel Superoxide Dismutase

“…The resulting structures showed little effect by addition of the proton, and in fact produced shorter Ni-S bond lengths. This is consistent with model studies that involve protonation [84], alkylation [56,[85][86][87], and oxidation [36,37,53,55,[88][89][90][91] of sulfur in nickel thiolate complexes and reveal that little structural change accompanies the chemical modifi cations. The computational results correlate well with the known model complexes and support the model for coordinated thiols in reduced NiSOD.…”

An Investigation of the Reactivity of [(diimine)(dithiolato)M] Complexes Using the Fukui Functions Concept

“…Grapperhaus et al have referred to a relative bonding situation using the term π-repulsion. [47] Moreover, since the above description of the HOMO is, by definition, consistent with the characteristics of the Fukui function f -, according to the frozen core approximation, it is clear that the driving force of the reaction with an electrophilic reagent is maximized in 4 (thermodynamic criterion), according to the series 4 Ͼ 3 Ͼ 2 (Pt Ͼ Ni Ͼ Pd). On the other hand, as the sulfur contribution to the HOMO is lower for Ni compounds (48.6 % vs. 51.7 % for Pd), an electrophilic attack on it could elongate the Ni-S bond and break it.…”

“…This trend is a direct consequence of a significant trans influence, with d C-S and d C-N being in the area of C-S(sp 2 ) and N-C(sp 2 ), respectively. An extensive analysis of the compounds' electronic structure has been presented elsewhere [28,47] and will not be discussed further here.…”

Mononuclear, Dinuclear, and Pentanuclear [{N,S(thiolate)}Iron(II)] Complexes: Nuclearity Control, Incorporation of Hydroxide Bridging Ligands, and Magnetic Behavior

“…Zinc, [1][2][3][4][5][6][7] nickel, [8][9][10][11][12] and iron [13][14][15][16][17][18][19][20] thiolate complexes have been made as models for mononuclear and polynuclear metalloenzyme active sites with RSÀM coordination. The alkylthiolate functionality is important because of its relevance to cysteinate ligation, but it is also quite challenging to control from a synthetic perspective.…”